The invention relates to a pneumatic tire having two different bead diameters and a method therefor.
In the early development of tires and wheels for automobiles, tires were sometimes made with different bead diameters to make easier the mounting of a tire over a cumbersome braking mechanism on the automobile. See for example U.S. Pat. Nos. 774,790; 870,248; 1,157,559; 2,347,622; 2,018,597; 2,028,702; 2,108,329; 2,843,171; French Patents 756,655; 849,466; 796,666, 818,460; Italian Patent 362,782; Swiss Patent 359,049; and German Patent 598,891.
In more recent years, it has been theorized by some that a dual bead diameter tire may have particular handling, ride, and/or treadwear advantages. See for example U.S. Pat. Nos. 3,656,532; 3,842,882; 3,974,870; and 4,124,679.
Prior art dual bead diameter tires, however, because of the one long sidewall and one short sidewall, tend to be unstable in use. On inflation, for example, the tread tends to shift to one side, causing the center of the tread to be out of alignment with the center of the tire. This causes one side of the tread to bear more of the weight of the vehicle than the other side of the tread. Also, because of the tire shift on the wheel during inflation, one bead becomes more generally aligned with the maximum width of the sidewall, making more probable the slipping of the bead off the wheel during cornering or when hitting ruts or potholes.
The prior art has tried, without full success, controlling the stability of such tires by (1) making the sidewalls equal length, (2) making the sidewalls different lengths where the shorter sidewall terminates where the equilibrium shape of the sidewall becomes perpendicular to the axis of rotation of the tire, (3) making sidewalls of different lengths where the contour lengths are substantially equal, and (4) by molding the tire in an asymmetrical mold.
It is an object of the present invention to provide a dual bead diameter pneumatic tire which has all the advantages expected of a dual bead diameter tire, but substantially eliminates the problems encountered by such tires in the past. Other objects of the invention will be apparent to those skilled in the art from the following specification and claims.